1. Field of the Invention
This invention relates to an apparatus and process for a temperature measuring pyrometer probe that measures gas temperatures above the melting point of conventional thermocouples and calculates and compensates for radiation heat losses and pneumatic cooling of the pyrometer probe.
2. Description of the Prior Art
U.S. Pat. No. 4,480,930 teaches a pulse cooled thermocouple temperature measuring apparatus. The apparatus includes a support member having rake channels. As taught by the '930 patent, each thermocouple is supported within a rake channel which has an open end exposed to hot gas. The thermocouple wires and the thermocouple junction are enclosed in mineral insulation which is encased in a steel sheath. To prevent melting, the thermocouple is cooled by pulsed cooling air flowing through the channels toward the thermocouples. A computing means responds to thermocouple signals to open a coolant valve so that cooling air may flow toward the thermocouple when the thermocouple temperature reaches a predetermined temperature. The computing means responds to the temperature signals and closes the cooling valve to enable a new temperature reading cycle after the thermocouple has cooled to a lower temperature. The computing means extrapolates temperatures which correspond to the temperature of the hot gas. The '930 patent teaches that extrapolation of the temperatures is based on the assumption of an exponential temperature curve. A disadvantage of the teachings of the '930 patent is that without air cooling the support member and the rake channels in which the thermocouple junctions are positioned, the system is severely limited to temperatures which slightly exceed the melting point of the materials. Another disadvantage is that the radiation heat transfer losses and pneumatic cooling of the system are assumed to be negligible and thus are not compensated.
The article by Gabriel, F. K., et al., "Fluid Pulsed Thermocouple Rake System for Automatic High Gas Temperature Measurements", American Society of Mechanical Engineers Paper No. 82-GT-107, 1982, teaches a multiple thermocouple pulse probe wherein each thermocouple operates in a transient mode up to a limiting temperature, at which point the thermocouple is cooled to a relatively low temperature in preparation for a subsequent transient heat-up cycle. The Gabriel et al. article does not teach any thermocouple junction or probe design which compensates for radiation heat transfer losses or pneumatic cooling of the probe channels.
The article by Kretschmer, D., et al., "The Pulsed Thermocouple for Gas Turbine Application", Journal of Engineering for Power, January 1977, pp. 1-10, teaches a mechanically pulsed, water cooled probe that is inserted into and out of a hot gas stream as a function of a predetermined temperature of the thermocouple. Gas is drawn into a sonic orifice of the probe. For the type of pulse thermocouple taught by the Kretschmer et al. article, it is assumed that radiation to the bead is very small due to the location of the thermocouple inside the probe and that any such heat losses should be taken into account through a calibration process. The effects of radiation are minimized by placing a shield around the thermocouple bead so that the bead is surrounded by walls having a temperature similar to that of the bead.
U.S. Pat. No. 3,111,032 teaches a water cooled temperature measurement apparatus for extending the range of a temperature sensor such as a thermocouple, which is used to measure temperatures of relatively hot liquids such as molten steel. The sensor is cyclically cooled to provide periods of exposure at a temperature lower than the measurement temperature. A disadvantage of the teachings of the '032 patent is that the apparatus does not account for radiation heat losses.
The NASA article by Glawe, G. E., et al., "A New Approach to the Pulsed Thermocouple for High Gas Temperature Measurements", NASA TMX-71883, presented at the 22nd International Instrumentation Symposium, San Diego, Calif., May 25-27, 1976, teaches a thermocouple that is cooled by a small jet of inert gas. Once the thermocouple is cooled, the cooling jet is shutdown and the thermocouple is allowed to again heat to near its melting point, at which time a temperature reading is taken and the thermocouple is again cooled. The article by Wormser, A. F. and Pfuntner, R. A., "Pulse Technique Extends Range of Chromel-Alumel to 7000.degree. F.", Instruments and Control Systems, May 1964, pp. 101-103, teaches a pulsed thermocouple system having a thermocouple, a coolant system and a computer. The coolant flow is periodically interrupted to expose the thermocouple to the gas being measured. Before the thermocouple reaches its critical melting temperature, the coolant flow is restored and the cycle is repeated.
U.S. Pat. No. 4,305,286 teaches a temperature sensor system that has a thermocouple encased in a protective tube of heat-resistant material, such as ceramic. The thermocouple reciprocates between a retracted position exterior of the reactor and a measurement point within the reactor.
U.S. Pat. Nos. 3,702,076, 3,877,307 and 3,942,123 all teach electronic thermometers which have digital displays. U.S. Pat. No. 3,878,724 teaches a method and apparatus for reducing the response time of a sensor, such as a medical probe thermometer, positioned in a medium under observation.